1. Field of the Invention
This invention relates to a fluid injection device and more particularly to fluid injection devices for use in internal combustion engines.
2. Description of the Prior Art
In internal combustion engines it is the current practice to inject fluid either at the inlet, in the form of fuel or combustion-supporting agents, or at the exhaust, where the injection as a rule takes the form of the admission of air for the after-combustion of the exhaust gases to reduce their pollution. Air injection at the exhaust, used on its own or in addition to catalysis systems, is one of the means used to reduce harmful emissions at the exhaust by oxidizing carbon monoxide and unburned hydrocarbons. It enables engines to run with levels of richness above 1, thus assisting high performance and also substantially reducing nitrogen oxide.
In the prior art systems air flow is independent of the phases of the cycle for each cylinder. Being essentially a function of the rotation conditions of the air pump, it is, if necessary, regulated globally for all cylinders in certain operational conditions (starting from cold, full load, etc.).
Among the fluid injection devices comprising conduits or channels discharging into at least one of the inlet or exhaust pipes of each engine cylinder, devices are known in which the fluid is injected at the level of the stop shoulder by which the valve seat is fitted into the cylinder head. Devices are also known in which the fluid is injected by means of the valve guide, either outside the latter between a portion of its fitting into the cylinder head and the cylinder head itself, or inside such guide, by means of a constriction of the diameter of a portion of the valve stem.
A serious disadvantage of these devices is that the fluid is injected at a relatively considerable distance from the valve head. Consequently, the valve head is not cooled in an optimum manner by the fluid, and fluid injection is not associated with the cyclic opening and closure phases of the valve. For each cylinder, the injection of a fluid such as air is continuous, while reaction with the gases leaving the cylinder can take place only during the exhaust phase -- i.e. one quarter of the engine cycle. During the three other phases -- i.e. three quarters of the cycle -- not only does the air flow fail to produce any further reaction, but produces a cooling which is prejudicial to the required effect. In view of this fact, selected of the air flow in this case is the result of a compromise between combustion efficiency during the exhaust phase and the risks of excessive cooling during the remainder of the engine cycle, so that the effect of after-combustion cannot be exploited to the maximum potential.
Moreover, in the prior art method last cited, there is a risk that the guidance and durability of the valve may be adversely affected by the intended reduction in the section of its stem, where a breakage can start.